Department of Phanerogamic Botany, Swedish Museum of Natural History, Svante Arrhenius väg 7, P.O. Box 50007 SE-104 05 Stockholm, Sweden.
Am J Bot. 2009 Jul;96(7):1361-71. doi: 10.3732/ajb.0800236. Epub 2009 Jun 10.
Flowers of Santalales remain largely unexplored with several questions of homology unanswered despite the large size of the order. Morphological and ontogenetic floral studies have the potential to identify new informative characters. We studied floral development in species of Loranthaceae, Santalaceae, Opiliaceae, and "Olacaceae" with scanning electron microscopy to clarify the origin and evolution of the perianth in Santalales. The perianth is either dichlamydeous or when monochlamydeous interpreted as sepals, petals, or tepals. A girdling calyculus of debatable origin is found in some clades. We show that species of Diogoa and Heisteria in "Olacaceae" have a dichlamydeous perianth, unlike Olax in which the calyx is replaced by a calyculus. The calyculus arises by development of two lateral primordia, supporting the hypothesis of bracteole origin. A calyculus with similar development is present in species of Loranthaceae and possibly of Opiliaceae, suggesting a position of Olax closer to these families than to traditional genera of "Olacaceae". The monochlamydeous perianth in Santalaceae is shown to correspond to petals of other members of Santalales. Flower ontogenetic evidence suggests a repeated loss of the calyx, replacement by a calyculus, and further loss, leading to monochlamydeous perianths in Santalaceae.
檀香目花卉的研究仍然很大程度上尚未被探索，尽管该目植物的规模庞大，但许多同源问题仍未得到解答。形态学和个体发生的花卉研究有可能确定新的信息特征。我们使用扫描电子显微镜研究了桑寄生科、檀香科、肉实树科和“铁青树科”的花卉发育，以阐明檀香目花被的起源和演化。花被要么是二唇形的，要么是单唇形的，被解释为萼片、花瓣或花被片。一些分支中存在起源有争议的环状花萼。我们表明，“铁青树科”中的 Diogoa 和 Heisteria 物种具有二唇形花被，而不同于 Olax，Olax 的花萼被花萼环所取代。花萼环由两个侧原基的发育产生，支持了小苞片起源的假说。在桑寄生科和可能的肉实树科的物种中存在具有相似发育的花萼环，这表明 Olax 的位置更接近这些科，而不是传统的“铁青树科”属。檀香科的单唇形花被被证明与檀香目其他成员的花瓣相对应。花的个体发生证据表明，花萼反复丢失，被花萼环取代，进一步丢失导致檀香科的单唇形花被。
